1. Field of the Invention
The present invention relates to a process for controlling a DC/DC voltage converter, or chopper, with inductive storage. More particularly, the invention relates to such a process which, in a known manner, operates according to cycles for transferring energy between a primary source and a secondary source, each cycle comprising a period of accumulation of magnetic energy in an inductive element from the primary source, followed by a period of restitution of this energy in the secondary source.
2. Discussion of the Background
DC/DC voltage converters with inductive storage comprise an inductive storage element placed between a primary circuit with a controlled switch interposed ahead of a power supply source and a secondary circuit with switch interposed ahead of a load. The primary circuit ensures, through the tripping of its switch, the control of the cycles for delivering energy from the power supply source to the inductive storage element whilst the secondary circuit ensures the control of the cycles for delivering energy from the inductive storage element to the load.
Originally, these DC/DC voltage converters used a fixed chopping frequency and possessed no regulation of their output voltage. The fixed chopping frequency was a beneficial characteristic when powering loads sensitive to radioelectric noise since the radioelectric noise of the converter remained confined within a small band around its chopping frequency and it was possible, by shifting this chopping frequency, to succeed in minimizing the influence of the radioelectric noise of the converter on its load by taking account of the latter's sensitive frequencies. On the other hand, the absence of output voltage regulation was very often a hindrance in so far as it was subject to sizeable fluctuations as a function of the variations in the power absorbed by the load and of the variations in voltage of the power supply source.
At first, provision was made, at the output of DC/DC voltage converters with inductive storage, for ballast-based voltage regulation in respect of loads sensitive to supply voltage variations. However, this resulted in a sizeable loss of efficiency. To solve this problem, DC/DC voltage converters with inductive storage were subsequently equipped with servocontrols for regulating their output voltage which essentially alter the duration of their cycle of energy delivery to their inductive storage element.
There are a large number of types of servocontrols for regulating output voltage for DC/DC converters with inductive storage. Among the most successful may be cited that described in French Patent Application FR-A-2 729 516. These output voltage regulating servocontrols are generally satisfactory and improve efficiency to a great extent. However, they cause a variation in the chopping frequency as a function of the power absorbed by the load and of the voltage of the power supply source. This variation in chopping frequency produces a broadening of the noise band of the converter, rendering the problems with radioelectric spurious interference of the loads more difficult to solve. Furthermore, it induces variations in the efficiency which decreases as the chopping frequency increases.
DC/DC voltage converters with inductive storage and output voltage servocontrol are well known, from the prior art, especially from German Patent DE-44 38 387, these converters operating at fixed frequency but posing problems both of efficiency and of radioelectric noise since they engender large current pulses.
These converters comprise, as is customary, an inductive storage element, a primary circuit with controlled switch interposed between a power supply source and the inductive storage element and a secondary circuit with switch interposed between the inductive storage element and a load. Moreover, in their primary circuit, they exhibit an overcurrent detector which causes the controlled switch to open in the event of an overcurrent, and in their secondary circuit they exhibit a device for short-circuiting the terminals of the inductive storage element triggered as a function of the instantaneous voltage appearing across the terminals of the load. Regulation of the voltage across the terminals of the load is obtained here by displacing the transition between the periods of accumulation and of restitution of energy from the inductive storage element in the course of each chopping cycle of constant duration. To do this, a short circuit is created, in the secondary circuit, earlier or later in each period of accumulation of energy in the inductive storage element, that is to say while the controlled switch of the primary circuit is conducting, this short circuit causing an overcurrent in the primary circuit and tripping the opening of the controlled switch by the overcurrent detector. This overcurrent pulse at each chopping cycle degrades the efficiency and increases the radioelectric noise of the converter.